1. Field of the Invention
The present invention relates to an extrusion die for manufacturing a metal hollow member such as an aluminum hollow member, a mandrel for the extrusion die, and a male die for the extrusion die.
2. Description of Related Art
For example, as shown in FIG. 14, a conventional extrusion die for manufacturing a hollow member 1 (see FIG. 13) includes a male die 101 for forming hollow portions 1a of the hollow member 1 and a female die 102 for forming the external peripheral portion of the hollow member 1. The female die 102 is fitted in an annular base portion 103 of the male die 101.
The male die 101 includes the aforementioned annular base portion 103 and a bridge portion 104 formed on the rear face (i.e., upstream-side surface) of the annular base portion 103. The bridge portion 104 includes a mandrel holding slit 105 extending in the fore-and-aft direction at the central portion thereof. Into this mandrel holding slit 105, a mandrel 108 having a mandrel main portion 106 with comb-shaped forming protrusions 107 is inserted from the rear side of the mandrel holding slit 105 and held therein. The female die 102 having a forming aperture 109 penetrated in the fore-and-aft direction of the female die 102 is fitted in a fitting aperture 110 formed in the axial center of the annular base portion 103 to be connected with the male die 101 concentrically. Thus, the forming gap 111 corresponding to the cross-section of the hollow member 1 to be extruded is formed between the forming protrusions 107 and the female-die forming aperture 109.
The forming protrusions 107 of the mandrel 108 are required to have such hardness that can bear high extrusion pressure at the time of extrusion. Accordingly, the forming protrusions 107 are usually made of super-hard material such as cemented carbide or ceramics and formed by an electric-spark forming method.
In a conventional die, however, since the forming protrusions 107 of the mandrel 108 are integrally formed at the tip of the mandrel main portion 106, the whole mandrel is made of super-hard material, resulting in an expensive component.
Furthermore, since the forming protrusions 107 are integrally formed on the mandrel main portion 106, damage of the forming protrusions 107 causes an exchange of the entire mandrel 108, causing increased running costs.
For example, in order to increase the number of hollow portions of the hollow member arranged side by side, it is necessary to increase the number of the forming protrusions 107 formed on the tip portion of the mandrel main portion 106 or decrease the thickness of each forming protrusion 107. However, there was a limitation to give further precise processing to the tip portion of the mandrel main portion 106.
It is an object of the present invention to provide an extrusion die for a hollow member which can decrease the costs for manufacturing the hollow member and for maintaining the extrusion die and can easily cope with more precise processing.
It is another object of the present invention to provide a mandrel for the aforementioned extrusion die.
It is still another object of the present invention to provide a male die for the aforementioned extrusion die.
According to the first aspect of the present invention, an extrusion die for a hollow member, comprises: a male die for defining a plurality of hollow portions of the hollow member, the male die including an annular base portion and a bridge portion bridging the annular base portion; a female die for defining an outer peripheral portion of the hollow member; and a mandrel having a plurality of forming protrusions, the mandrel being inserted and held in a mandrel holding slit formed in a center of the bridge portion in a fore-and-aft direction, wherein the mandrel includes a mandrel main portion divided into a plurality of divided members and a plurality of rigid pins each arranged in a fore-and-aft direction of the mandrel main portion, and wherein the plurality of rigid pins are pinched by and between the divided members of the mandrel main portion with tip portions of the plurality of rigid pins protruding from a front end of the mandrel main portion, whereby the plurality of tip portions constitute the plurality of forming protrusions.
With this extrusion die, the mandrel main portion is divided into a plurality of divided members and the rigid pins are pinched by and between the divided members with tip portions of the rigid pins forming the forming protrusions protruding from a front end of the mandrel main portion. Accordingly, the mandrel main portion can be made of relatively cheap hard material such as die steel by employing the rigid pins made of super-hard materials. This decreases the entire costs for the mandrel.
According to the second aspect of the present invention, a mandrel for use in an extrusion die for extruding a hollow member, the mandrel comprises: a mandrel main portion which is divided into a plurality of divided members; and a plurality of rigid pins each disposed in a fore-and-aft direction of the mandrel main portion, wherein the plurality of rigid pins are pinched by and between the divided members of the mandrel main portion with tip portions of the plurality of rigid pins protruding from a front end of the mandrel main portion, whereby the plurality of rigid pins constitute forming protrusions.
With this mandrel, it is possible to properly perform precise processing of the hollow member by the extrusion die.
According to the third aspect of the present invention, a male die for an extrusion die, wherein the male die defines a plurality of hollow portions of a hollow member and is combined with a female die defining an outer peripheral configuration of the hollow member, the male die comprises: an annular base portion; a bridge portion bridging the annular base portion; and a mandrel having a plurality of forming protrusions, the mandrel being inserted and held in a mandrel holding slit formed in a center of the bridge portion in a fore-and-aft direction, wherein the mandrel includes a mandrel main portion divided into a plurality of divided members and a plurality of rigid pins each arranged in a fore-and-aft direction of the mandrel main portion, and wherein the rigid pins are pinched by and between the divided members of the mandrel main portion with tip portions of the rigid pins protruding from an front end of the mandrel main portion, whereby the tip portions constitute the forming protrusions.
This male die can constitute the aforementioned extrusion die.
Other objects and the features will be apparent from the following detailed description of the present invention with reference to the attached drawings.